Increasing Voltage Levels Research Articles

Methods of improving the power supply reliability of industrial site

Ensuring reliability is one of the most important problems in the creation and operation of any technical system. It is especially relevant for complex systems such as power supply systems. A modern industrial site from the power supply point of view is a complex technical system of hazardous industrial facilities, the technological processes continuity and safety of which directly depends on the power supply reliability. Electricity receivers of the considered industrial site in terms of power supply reliability belong to the second category. The task of ensuring the power supply reliability includes a whole range of technical, economic and organizational measures aimed at reducing damage from disruption of the electricity consumers’ normal operation. In addition, in modern market conditions, the power supply reliability is inextricably linked with the economic performance and industrial enterprises energy security. The paper proposes to modernize the industrial site power supply circuit, using the existing standby diesel power plant, which would automatically provide the industrial site power supply in automatic mode in case of disappearance, decrease, increase in voltage level, phase failure, and the phase sequence violation of the three-phase supply voltage on the busbar sections TP-1, TP-2 site. It is obvious that with the existing power supply scheme of the industrial site, the manual switching sequence, control over the backup diesel power plant operation, the normal power supply scheme restoration, it takes an average of 2.5 hours, which is not desirable, especially in winter. Therefore, it is necessary to introduce at the industrial site production control devices for the reserve automatic transfer, which ensure the power supply restoration to the industrial site in automatic mode.

Three-dimensional calculation physical model for corona onset characteristics of AC grading rings

Corona discharge on the surface of power transmission and transformation fittings becomes increasingly serious with increasing voltage levels, especially for many grading rings in transformer substations. With the enhancement of people’s environmental awareness, the environmental protection administration requires noise and electromagnetic environment at transformer substations shall meet relevant standards. In order to suppress corona discharge on the surface of a grading ring, it is necessary to study its corona onset characteristics. Considering the basic physical process of the corona discharge, in this study, the electric field intensity is first calculated at any point in the space around the grading ring through ring charge simulation. Then, based on the theory of secondary electron emission, criteria for calculating the onset voltage of negative corona of the grading ring are derived, leading to an area factor of a photon absorption function suitable for the grading ring. In this way, a three-dimensional (3D) calculation physical model of the corona onset suitable for the grading ring is developed. This study calculates the corona onset voltage and field intensity of the grading ring under the typical working conditions by using the proposed 3D calculation physical model of the corona onset. The calculation results are compared with test results of the corona onset voltage and field intensity of grading rings in an outdoor 750 kV transformer substation in an ultrahigh voltage (UHV) alternating current (AC) test base. Furthermore, the simulation results of the area factor of the photon absorption function, electron collision coefficient, electron adsorption coefficient, and effective ionization coefficient in the 3D calculation physical model are obtained. In this way, the accuracy of the 3D calculation physical model of the corona onset proposed in this paper is verified. The research results can provide a theoretical basis for the corona prevention design of grading rings in extra high voltage/UHV AC power transmission and transformation projects.

Optimum sitting and sizing of WTs, PVs, ESSs and EVCSs using hybrid soccer league competition-pattern search algorithm

With increasing environmental sensitivity and developing technology, Distributed Generations (DGs), Electric Vehicles Charging Stations (EVCSs), and Energy Storage Systems (ESSs) have been significant part of a distribution grid. However, inappropriate sitting and sizing of these components may negatively affect the performance of distribution grid. Besides, efficient operation of distribution grid can be achieved by only choosing the proper sizes of DGs, EVCSs, ESSs and placing them at the appropriate locations in the grid. In this paper, a weighted sum multi-objective function is formulated for reducing power loss, increasing voltage level and integration capacity of DGs, EVCSs, ESSs, simultaneously. Also, hybrid Soccer League Competition–Pattern Search (hSLC-PS) optimization algorithm is proposed to improve fine-tune performance of optimization. Simulations are carried out considering time-varying and stochastic nature of Photovoltaics (PVs) and Wind Turbines (WTs) generations and EVCSs load demand. The performance of the proposed method has been investigated on 33-bus and 85-bus test systems under different conditions and the statistical results are compared to SLC and Grey Wolf Optimization (GWO) algorithms to validate the effectiveness of the proposed algorithm. Statistical results clearly reveal the superiority of hSLC-PS in simultaneous sitting and sizing of DGs, EVCSs and ESSs.

Обоснование схемы активного фильтра гармоник на основе гибридного каскадного инвертора

With an increase in the number of levels in the inverter, the circuit becomes more complicated, the number of semiconductor switches increases. Therefore, topologies, which make it possible to obtain an increase in voltage levels with a decrease in the number of semiconductors, to increase the performance and reliability of the system, are of great interest. The paper proposes a scheme of a hybrid cascade inverter, considers a method of pulse-width modulation based on a carrier, and presents a block diagram of an algorithm for generating reference modulating signals in an optimized method of pulse-width modulation. To control a hybrid inverter as part of an active harmonic filter, a method of pulse-width modulation of the carrier is proposed. It allows reducing the common-mode voltage, switching losses, and minimizing current and voltage harmonics. The paper describes the PWM algorithm, on the basis of which the control signals are modulated and then compared with a triangular carrier to generate a sequence of pulses that turn on or turn off semiconductor switches. The purpose of the proposed solutions is to improve harmonic distortion caused by non-linear load in a 0.4 kV low-voltage system. The results of modeling the proposed active harmonic filter circuit are presented. Based on the studies performed, it is shown that the use of an active harmonic filter based on a 5-stage hybrid inverter with pulse-width modulation control is an effective means of filtering higher harmonics on 0.4 kV low voltage buses in the presence of a nonlinear load, which allows solving the problem of eliminating the impact of higher harmonics on the production activities of the enterprise.

Calculation of Electric Field on Substation Equipment considering AC Ion Flow Field

With the increase of voltage levels in substation corona discharge on the surface of high voltage conductors and equipment in substations becoming more and more severe, the influence on the electromagnetic environment around substations is becoming more and more obvious. In order to study the influence of corona discharge on the ground electric field under substation equipment in AC substations, this paper proposes an improved method based on Abdel-Salam’s calculation of the ion flow field on AC power lines. By redefining the criterion of corona onset and the amount of emission charge and combining with the migration, motion, and recombination of the space charge, a new model which can be applied to the calculation of AC ion flow field electric field of multiphase bundle conductors in substations is established. The calculation results of the ground power frequency electric field of the conductor at the typical tower in the light, medium, and heavy ice regions of 750 kV typical AC transmission project show that the ground electric field gradually decreases with the increase of conductor height. At the same conductor height, the ground electric field strength in the heavy ice region is the largest, while under the conductor in a light ice region, it is the smallest, and the minimum allowable conductor-to-ground distance can be concluded that the national standard limit value is not exceeded when the conductor-to-ground distance in light ice region is 24.5 m, the conductor-to-ground distance in medium ice region is 25.5 m, and the conductor-to-ground distance in heavy ice region is 26 m.

A novel complex current ratio-based technique for transmission line protection

With respect to sensitivity, selectivity and speed of operation, the current differential scheme is a better way to protect transmission lines than overcurrent and distance-based schemes. However, the protection scheme can be severely influenced by the Line Charging Capacitive Current (LCCC) with increased voltage level and Current Transformer (CT) saturation under external close-in faults. This paper presents a new UHV/EHV current-based protection scheme using the ratio of phasor summation of the two-end currents to the local end current, instead of summation of the two-end currents, to discriminate the internal faults. The accuracy and effectiveness of the proposed protection technique are tested on the 110 kV Western System Coordinating Council (WSCC) 9-bus system using PSCAD/MATLAB. The simulation results confirm the reliable operation of the proposed scheme during internal/external faults and its independence from fault location, fault resistance, type of fault, and variations in source impedance. Finally, the effectiveness of the proposed scheme is also verified with faults during power swing and in series compensated lines.

Optimization of decontamination conditions for Aspergillus flavus inoculated to military rations snack and physicochemical properties with atmospheric cold plasma

AbstractIn this study, the effectiveness of ACP in inactivating Aspergillus flavus inoculated to military rations snack using response surface methodology (RSM) was investigated. Additionally, the effect of this treatment on the total count and yeast–mold count, as well as some quality properties of military rations snack, was examined. RSM was applied to study the voltage effects (5–15 kV), the distance between ACP emitter and sample (3–7 cm), and different treatment time (2–10 min) on the physicochemical properties of the military rations snack. Increasing voltage and time, together with reducing distance, caused a decrease in A. flavus, total count, yeast and mold count, total aflatoxin, as well as color difference. The peroxide value also increased with increasing voltage levels. The optimum conditions for treated military rations snack by ACP are as follows: a system voltage of 9 kV, a distance of 3 cm between the sample and the emitter, and a time of 6 min. Under these conditions, the responses, including the utmost reduction of 4.31 log CFU/g for the total count, 4.64 log CFU/g for yeast–mold count, and 2.98 log CFU/g for A. flavus were found from starting level of 5.2, 2, and 3.1 log CFU/g, respectively. It was found that snack samples had a 3.66% decrease in moisture content, 76.13% decrease in total aflatoxin, 3.01% increase in color difference, and 0.22 meq O2.kg/oil increase in peroxide value as a result of ACP application. ACP has the potential to increase microbiological safety by maintaining desirable quality properties in military rations snack.

Analysis of Most Optimal Multi-unit Multi-level Inverter Having Minimum Components and Lower Standing Voltage

Most of the asymmetrical reduced-component multi-level inverters (MLIs) can generate their maximum possible voltage levels; however, their total standing voltage (TSV) is comparatively higher. Here, a single-phase, multi-unit MLI configuration is proposed that can generate a maximum number of output voltage levels using minimum components and achieve lower TSV. Here, a single-phase generalized MLI unit is proposed to generate a more number of output voltage levels using lesser components and to achieve lower TSV. The inverter is further extended to a cascaded multi-unit MLI for high power applications. Further, a most optimal generalized multi-unit MLI is derived from the generalized topology that has designed with a minimum component and TSV for maximum voltage levels. The performance of the proposed MLI is compared with other similar existing MLIs in terms of the number of switches, the number of DC sources and TSV with an increase in voltage levels to prove its superiority. Further, a comparative study of voltage stress experienced on the highest voltage rated switches of the proposed most optimal MLI and the most popular CHB trinary is done for an increasing number of levels. The TSV of the proposed 11-level inverter is calculated as 21V DC, which is much smaller as compared to the similar existing topologies. A MATLAB/Simulink based simulation and corresponding experimental results of the 11-level and 47-level inverters are presented at different modulation indices as well as under load variations to verify their effectiveness.

Analysis on corrosion of flat steel used in grounding grid for 220 kV substation

Grounding grid plays an important role in protection of main device for power system. With the increase of power capacity and voltage level, the safety of grounding grid is particularly important. In this paper, the seriously corroded flat steel of grounding grid in 220kV substation was investigated by means of different test methods. The result showed that electrode potentials difference existed between different locations on the surface of the buried grounding electrode was the major reason to cause electrochemical corrosion. Meanwhile, higher sulphur and chlorine content of the soil around the substation caused by long-term industrial pollution, led to rapid depletion of zinc coating and acceleration of corrosion process of grounding material. Additionally, effective suggestions were presented in order to reduce the grounding resistance and improve the anti-corrosion performance.

A CMOS Image Sensor Pixel Combining Deep Sub-Electron Noise With Wide Dynamic Range

This letter introduces a 5-transistors (5T) implementation of CMOS Image Sensors (CIS) pixels enabling the combination of deep sub-electron noise performance with wide dynamic range (DR). The 5T pixel presents a new technique to reduce the sense node capacitance without any process refinements or voltage level increase and features adjustable conversion gain (CG) to enable wide dynamic imaging. The implementation of the proposed 5T pixel in a standard 180nm CIS process demonstrates the combination of a measured high CG of 250 ${\mu V/e^{-}}$ and low CG of 115 ${\mu V/e^{-}}$ with a saturation level of about 6500 e− offering photo-electron counting capability without compromising the DR and readout speed.

Simplified Predictive Duty Cycle Control of Multilevel Converters With Internal Identical Structure

Classical finite control set model predictive control of multilevel converters faces two major limitations: heavy computation burden and low steady-state performance. On the other hand, the internal paralleled or cascaded identical structure is extensively employed in multilevel converters as the voltage level increases. Taking advantage of the internal identical structure in multilevel converters, a simplified predictive duty cycle control method for multilevel converters is proposed in this article. First, a series of switching pairs with the identical structure are modeled as a virtual switching state, and the number of the corresponding voltage vectors can be significantly reduced. Then, a least-square optimization problem is formulated to calculate the duty cycles for optimal output current tracking using these virtual voltage vectors. The output current quality is enhanced due to the employment of the interleaved output voltage stage with phase-shifted pulsewidth modulation. As the number of voltage vectors is significantly reduced, the computation burden is drastically reduced. The proposed method can be applied in various multilevel topologies with internal identical structures. Simulation and experimental results on the multilevel converters with internal cascaded/paralleled identical cells are presented to verify the good performance and application value of the proposed method.

Nanodielectrics

Polymers and insulating fluids as dielectrics and electrical insulation are the cornerstones of electrical as well as electronics engineering. The former because of their excellent electrical properties, ease of processing and low cost, and the latter due to their superior heat transfer capabilities. With the increasing requirements for transfer power, hence increasing voltage level of power systems, the properties of dielectrics, in particular high-field electrical properties, need to be significantly improved to fulfill the requirements for operational safety and reliability of power systems in the long term. However, the techniques used for large scale production of dielectrics meet a bottleneck, when further improvement of electrical properties are necessary, while maintaining key thermo-mechanical properties. Fortunately, nanotechnology may provide solutions to this problem. Some nanoparticles have been identified to exhibit great potential for improving the electrical properties of dielectrics. In this case the nanoparticles-containing dielectric polymers they have been termed as Nanodielectrics, while liquid insulation systems with nanoscale matter are referred to as Nanofluids.

Simulation and Experimental Investigation on Carbonized Tracking Failure of EPDM/BN-based Electrical Insulation.

Ethylene propylene diene monomer (EPDM) is broadly employed as an insulating material for high voltage applications. Surface discharge-induced thermal depolymerization and carbon tracking adversely affect its performance. This work reports the electrical field modeling, carbon tracking lifetime, infrared thermal distribution, and leakage current development on EPDM-based insulation with the addition of nano-BN (boron nitride) contents. Melt mixing and compression molding techniques were used for the fabrication of nanocomposites. An electrical tracking resistance test was carried out as per IEC-60587. Simulation results show that contamination significantly distorted the electrical field distribution and induced dry band arcing. Experimental results indicate that electric field stress was noticed significantly higher at the intersection of insulation and edges of the area of contamination. Moreover, the field substantially intensified with the increasing voltage levels. Experimental results show improved carbonized tracking lifetime with the addition of nano-BN contents. Furthermore, surface temperature was reduced in the critical contamination flow path. The third harmonic component in the leakage current declined with the increase of the nano-BN contents. It is concluded that addition of nano-BN imparts a better tracking failure time, and this is attributed to better thermal conductivity and thermal stability, as well as an improved shielding effect to electrical discharges on the surface of nanocomposite insulators.

Investigation of Standalone Solar Photovoltaic Water Pumping System With Reduced Switch Multilevel Inverter

Solar photovoltaic powered water pumping systems are becoming very successful in regions where there is no opportunity for connecting the grid. The photovoltaic technology converts solar energy into electrical energy for operating DC or AC motor-based water pump. In the case of a solar AC motor water pump, it engages two energy conversion stages (DC-DC and DC-AC) in the power conditioning unit. This usually resulted in increased size, cost, complexity and decreases efficiency of the entire system. In addition, the existing two-level inverter (DC-AC) stage generates higher harmonics in output voltage that deteriorates AC motor performance. As a consequence, a single energy conversion stage with more than two-level output voltage could be possible by utilizing multilevel inverters which replaces two-level inversion stage easily to get higher levels of output voltages as well for extracting best results from the motor. Moreover, they can able to operate with reduced switching frequency that certainly reduces switching losses. Still, the increased voltage levels comprise a higher number of power semiconductor switches, cumulative voltage stress and switching losses are making the system more complicated. In this paper an innovative seven-level inverter with five switches had been taken to investigate 0.5 H. P single phase induction motor water pump. This topology ensures minimum switching losses, lowering size along with less installation cost. In order to provide better insight into the working and performance of this proposed topology the simulation results performed in the MATLAB / Simulink environment and hardware implementation are depicted.

Performance analysis of dynamic CMOS circuit based on node‐discharger and twist‐connected transistors

The incessant growth of devices such as mobile phones, digital cameras, and other portable electronic gadgets has led to a higher amount of research being dedicated to the low power digital and analogue circuits. In this study, a low power-delay-product (PDP) dynamic complementary metal oxide semiconductor (CMOS) circuit design using small swing domino logic with twist-connected transistors is proposed. An improvement in PDP can be achieved by using a node-discharger circuit in the conventional design. The conventional benchmark and modified circuits are implemented in 90 nm CMOS technology with different power supplies, i.e. 1.2, 1, and 0.9 V. Furthermore, a decrease in voltage level for logic ‘1’ and an increase in voltage level for logic ‘0’ is achieved while maintaining the logic threshold accordingly at half of the supply voltage. So, the output voltage swing is reduced and the unnecessary nodes of the pull down network get discharged in pre-charge phase, eventually leading to an improvement when compared with conventional design in overall PDP by 43.21 and 46.83% for two inverted two-input and three-input AND gate dynamic benchmarks, respectively, for a power supply of 1 V.

Detection of DC series arc in more electric aircraft power system based on optical spectrometry

Series arcing faults have been recognised as a hazardous phenomenon in the power system of more electric aircraft (MEA), especially with the increasing voltage level and power supply. Instead of the electrical method, the optical method can be used as an approach to detect arc fault with the advantages of fast response and immunity to electromagnetic interference. It is the basis of optical arc detection to determine the distribution spectrum range of direct current (DC) arc fault. Aiming at series arc optical detection in the MEA DC system, a DC series arc test platform was established to measure the series arc spectrum. The spectrum was disassembled though empirical mode decomposition to extract characteristic wavelengths of arc light and de-noised by means of wavelet decomposition and reconstruction (wavelet transformation) to reduce equipment noise. To resolve the baseline drift, the baseline of the arc spectrum measured was calculated and corrected based on Savitzky−Golay. The experimental results indicate that there are several series arc characteristic spectra of the MEA DC system, including 309.3 and 324.5 nm in the ultraviolet range. Moreover, the arc spectrum with different metals, copper and aluminium, were contrasted, indicating the arc spectral behaviour is related to the melting/boiling point and chemical properties of the anode material. The measurement of the series arc spectrum makes it more effective to apply optical detection in the MEA discharging faults diagnosis.

A novel control strategy based on hybrid instantaneous theory decoupled approach for PQ improvement in PV systems with energy storage devices and cascaded multi-level inverter

This paper suggests an innovative control architecture based on hybrid instantaneous theory (HIT) decoupled method for improved power quality (PQ) in a photovoltaic (PV) based microgrid utilizing energy storage devices (ESD). Further, to enhance the PV-ESD performance, an eleven-level cascaded inverter (ECI) with compact size, cost, and increase in voltage level is proposed. By considering the simplicity in design and wider application, an improved perturb and observe (IP&O) method is implemented to operate the PV-ESD system at its optimum power point (OPP). In addition to that, for achieving an improved energy management, a battery-based ESD is integrated into the system. Furthermore, the use of grid LCL filter in PV is investigated with the proposed control law design to reduce the harmonic content. To verify the robustness of the HIT approach based on the harmonics and nonlinearity, various test conditions have been examined under different cases ranging from varying environmental conditions, varying grid demand and ESD charging and discharging situations by using MATLAB/Simulink software.

Polycyclic Compounds Affecting Electrical Tree Growth in Polypropylene Under Ambient Temperature

Polypropylene (PP) has great potential to be used as recyclable high-voltage direct current (HVDC) cable insulation material. Electrical tree is the key factor that leads to cable insulation failure and limits the increase of HVDC transmission voltage level. In this study, three different polycyclic compounds, namely 4,4'-bis(dimethylamino)phenylazo, 2-hydroxy-2-phenylacetophenone and 4-phenylbenzophenone, are added into PP matrix with the addition content of 0.1 wt%. The electrical treeing experiments are conducted under impulse superimposed DC voltage at 30, 70 and 90 °C. Then the polycyclic compound with the best effect on inhibiting electrical tree is selected, and its filling ratio is further changed from 0.1 wt% to 0.3 wt% to get the optimal inhibition effect. It is found that the addition of 2-hydroxy-2-phenylacetophenone can inhibit the electrical tree degradation. However, the addition of 4-phenylbenzophenone and 4,4'-bis(dimethylamino)benzene will increase the electrical tree length and accumulated damage. As the content of 2-hydroxy-2-phenylacetophenone increases, the electrical tree length and accumulated damage decrease firstly, and then increase. The effect of polycyclic compounds on the electrical tree degradation is affected by the relative polarity of impulse superimposed DC voltage and temperature. The experimental results reveal that adding 0.1 wt% 2-hydroxy-2-phenylacetophenone polycyclic compound to PP can effectively inhibit the electrical tree degradation, which has great potential for application in recycle HVDC cables.

Physical interpretation of the floating electrode defect patterns under AC and DC stress conditions

Partial discharge is a prevalent phenomenon under high voltage (HV) where the discharge partially bridges the gap between two electrodes. At increasing voltage levels, physical dimensions and distances between the electrical parts become critical. Designing electrical components for such high voltages and planning of high voltage laboratories/tests need to deliberate this aspect as it could lead to possible complications such as partial discharges (PD) from the floating metal components. Floating electrodes under AC voltages are associated with a distinctive PRPD pattern. However, there is a lack of literature on the physical interpretation of this pattern. Likewise, under DC voltages, no consistent explanation towards the defect behavior has been reported. Therefore, this paper presents an in-depth study of the floating electrode defect configuration under AC and DC voltages. Subsequently, it provides the physical interpretation of the discharge patterns obtained through the stepwise description of the discharge stages under both conditions. By formulating criteria for repetitive discharges and presenting novel PD fingerprints for DC floating electrode configuration, the outcomes published in this paper contribute towards prospective PD defect identification tools under HVDC.

Microbial fuel cells directly powering a microcomputer

Many studies have demonstrated that microbial fuel cells (MFC) can be energy-positive systems and power various low power applications. However, to be employed as a low-level power source, MFC systems rely on energy management circuitry, used to increase voltage levels and act as energy buffers, thus delivering stable power outputs. But stability comes at a cost, one that needs to be kept minimal for the technology to be deployed into society. The present study reports, for the first time, the use of a MFC system that directly and continuously powered a small application without any electronic intermediary. A cascade comprising four membrane-less MFCs modules and producing an average of 62 mA at 2550 mV (158 mW) was used to directly power a microcomputer and its screen (Gameboy Color, Nintendo®). The polarisation experiment showed that the cascade produced 164 mA, at the minimum voltage required to run the microcomputer (ca. 1.850 V). As the microcomputer only needed ≈70 mA, the cascade ran at a higher voltage (2.550 V), thus, maintaining the individual modules at a high potential (>0.55 V). Running the system at these high potentials helped avoid cell reversal, thus delivering a stable level of energy without the support of any electronics.